Epichlorohydrin rubber, chlorine-containing acrylic rubber, etc. have been heretofore widely used for molded articles, such as hoses and sealing parts, because they are excellent in various properties, such as oil resistance, heat resistance, weathering resistance, ozone resistance and compression set.
In general, halogen-containing crosslinking polymers, such as the epichlorohydrin rubber and the chlorine-containing acrylic rubber, are often stored in the form of compositions obtained by adding crosslinking additives, such as crosslinking agent and crosslinking accelerator, to the polymers.
When diene type rubber compositions or chlorine type rubber compositions containing vulcanizing additives, such as vulcanizing agent and vulcanization accelerator, are stored, vulcanization generally proceeds slowly, and as a result, changes, e.g., increase of viscosity, reduction of scorch time and decrease of vulcanizing rate, are brought about to thereby lower processability of the compositions into molded articles or properties of the vulcanization products. From the viewpoint of retention of storage stability, these changes are desired to be small. If the vulcanization additives are not added, these changes are small. From the viewpoint of productivity, however, curable compositions in which the vulcanization additives are added in advance are generally employed, and therefore, it becomes important to improve storage stability of the compositions containing the vulcanization additives.
As the vulcanization additives for the diene type rubbers or the chlorine type rubbers, polythiol compounds, such as dithiol compounds and trithiol compounds, are conventionally known.
These polythiol compounds, however, have high reactivity, so that when the rubbers and the vulcanization additives are kneaded and processed, premature vulcanization sometimes takes place, or even if kneading can be carried out smoothly without premature vulcanization, gelation sometimes takes place during the subsequent storing stage. Thus, the compositions have a problem of lack of storage stability even if the properties of the resulting cured products are excellent.
As the crosslinking additives for the halogen-containing crosslinking polymers, triazinethiols are known.
The triazinethiols, however, have high reactivity and high crosslinking rate, so that when the rubbers and the crosslinking additives are kneaded and processed, premature crosslinking sometimes takes place, or even if kneading can be carried out smoothly without premature crosslinking, gelation sometimes takes place to increase viscosity in the subsequent storing stage, or partial crosslinking is promoted. That is to say, scorching is liable to occur, and hence, molding troubles are sometimes brought about.
On this account, an attempt to use a premature vulcanization inhibitor in combination to improve storage stability has been made. By the use of the premature vulcanization inhibitor in combination, however, problems of decrease of vulcanizing rate and deterioration of heat resistance are brought about.
For controlling the crosslinking rate, there has been also made an attempt to add metal oxide, metal hydroxide, carbonate, organic acid salt or the like and to select the type of metal, type of counter ion, etc. according to the reactivity of the halogen-containing crosslinking polymers and the reactivity of the triazinethiols. However, if satisfactory crosslinking rate is intended to be obtained, the scorch time is sometimes shortened.
Accordingly, there has been desired development of a novel thiol compound derivative capable of providing a rubber composition or a resin composition having excellent storage stability, processability and curability without using a premature vulcanization inhibitor that exerts evil influences on the properties of a cured product of a diene type rubber composition, a chlorine type rubber (halogen-containing crosslinking polymer) composition or the like. There has been also desired development of a curable composition having storage stability and moderate crosslinking rate and capable of providing a crosslinked product having excellent physical properties with a good balance.
The present inventors have earnestly studied to solve such problems as mentioned above, and as a result, they have found that by the use of, as a crosslinking agent, a thiol compound derivative wherein a thiol compound is protected by a protective group of vinyl ether or the like, a curable composition having excellent storage stability and crosslinking rate and capable of providing a crosslinked product of excellent physical properties can be obtained without using a premature vulcanization inhibitor that exerts evil influences on the properties of a cured product of a halogen-containing crosslinking polymer composition or a diene type rubber composition. Based on the finding, the present invention has been accomplished.
It is an object of the present invention to provide a novel thiol compound derivative capable of providing a rubber composition or a resin composition having excellent storage stability, processability and curability. It is another object of the invention to provide a curable composition comprising a halogen-containing crosslinking polymer and having a good balance of storage stability, crosslinking rate and physical properties of its crosslinked product. It is a further object of the invention to provide a molded product of the curable composition.